Yersinia Enterocolitica and Yersinia Pseudotuberculosis
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4 Yersinia enterocolitica and Yersinia pseudotuberculosis Maria Fredriksson-Ahomaa 1. CLASSIFICATION AND IDENTIFICATION Yersinia enterocolitica and Yersinia pseudotuberculosis are included in the genus Yersinia. These species were formerly included in the genus Pasteurella and later placed into the genus Yersinia, named in honor of the French bacteriologist A. J. E. Yersin, a discoverer of the plague bacillus (1). Y. pseudotuberculosis was the first species identified in this genus (2). This organism was described in 1889 as a disease in guinea pigs. How- ever, Y. pseudotuberculosis has shown to be the ancestor of Y. pestis, which was the cause of pandemic plague already during 541–767 AD (3). The Y. enterocolitica was identified in 1939 and named by Frederiksen in 1964 (4). The genus Yersinia is presently composed of 11 species, three of which can cause disease in humans and animals: Y. enterocolitica, Y. pseudotuberculosis, and Y. pestis (5–8). The three pathogenic species, the enteric foodborne pathogens Y. enterocolitica and Y. pseudotuberculosis, and Y. pestis are invasive pathogenic bacteria, which have a common capacity to resist nonspecific immune response and are lymphotrophic (9). These three pathogenic species differ considerably in invasiveness. While Y. enterocolitica and Y. pseudotuberculosis can cross the gastrointestinal mucosa to infect underlying tissue, Y. pestis is injected into the body through an insect bite, and thus, does not require penetrating any body surface on its own (9). The genus Yersinia is classified into the family Enterobacteriaceae, a group of Gram- negative, oxidase-negative and facultatively anaerobic bacteria. All bacteria, belonging to the genus Yersinia, are catalase-positive, nonspore-forming rods or coccobacilli of 0.5–0.8 × 1–3 Rm in size (5). These bacteria are lactose-negative and have the ability to grow at 0–4°C. Y. enterocolitica and Y. pseudotuberculosis are urease-positive and can be differentiated from other urease-positive Yersinia species on the basis of Voges–Proskauer test and their ability to ferment sorbitol, rhamnose, sucrose, and melibiose (Table 1). Y. enterocolitica is a heterogeneous species, which can be divided into six biotypes (1A, 1B, 2–5) on the basis of variations in biochemical reactions (10). Subdivision into these six biotypes can be done using the following reactions: pyrazinamidase activity, esculin hydrolysis, tween-esterase activity, indole production, and xylose and trehalose acidi- fication (Table 2). Biotypes 1B and 2–5 include strains that are associated with disease in man and animals when biotype 1A consists of nonpathogenic strains. However, strains From: Infectious Disease: Foodborne Diseases Edited by: S. Simjee © Humana Press Inc., Totowa, NJ 79 80 Fredriksson-Ahomaa Table 1 Biochemical Differentiation of Urea-Positive Yersinia Species After Incubation at 25°C for 18–20 h Reaction Voges– Species Proskauer Sorbitol Rhamnose Sucrose Melibiose Y. enterocolitica ++ + Y. pseudotuberculosis +/+/ Y. frederiksenii ++++ Y. intermedia +++++ Y. kristensenii + Y. aldovae +++ Y. rohdei + ++/ Y. mollaretii + + Y. bercovieri + + Table 2 Biochemical Tests Used for Biotyping Y. enterocolitica and Y. pseudotuberculosis Isolates Y. enterocolitica Y. pseudotuberculosis Reactiona BTb1A BT1B BT2 BT3 BT4 BT5 BT1 BT2 BT3 BT4 Melibiose + + Citrate + Raffinose + Pyrazinamidase + Esculin + ++++ Tween ++ Indole +++ Xylose ++++ ++++ Trehalose +++++ ++++ aAll tests done at 25°C. bBT, biotype. of biotype 1A have constituted a sizeable fraction of strains from patients with gastro- enteritis (11,12). Neubauer et al. (13,14) have demonstrated on the basis of the different DNA–DNA hybridization values and the 16S rRNA gene sequences that Y. enterocolitica should be divided into two subspecies, with one subspecies consisting of strains of biotype 1B, and the other of the remaining strains. Compared to Y. enterocolitica is Y. pseudotuberculosis a phenotypically more homo- geneous species. Nevertheless, Y. pseudotuberculosis can be divided into four biotypes according to their behavior in citrate, melibiose, and raffinose (15) (Table 2). No cor- relation of pathogenicity of Y. pseudotuberculosis with biotype was found in this study. However, melibiose-positive strains (biotypes 1 and 4) have shown to be more pathogenic than melibiose-negative strain (biotypes 2 and 3) (16). Yersinia 81 Table 3 Distribution of Pathogenic Y. enterocolitica Belonging to Different Bio-, Sero- and Phage Types Biotype Serotype Phagetype Host Distribution 1B O:4,32 Man United States O:8 X Man, pig, wild rodents Europe, Japan, North America O:13 Man, monkey North America O:18 Man United States O:20 Man, rat, monkey United States O:21 Man, rat flea North America 2 or 3 O:5,27 X Man, pig, dog, monkey Australia, Europe, Japan, North America O:9 X Man, pig, cattle, goat, Australia, Canada, Europe, dog, cat, rat Japan 3 O:1,2,3 I Chinchilla Europe, United States O:3 II Man, pig, dog Japan Man, pig, rabbit, rat Korea 4 O:3 VIII Europe, Japan IXA Man, pig, dog, cat, rat South Africa IXB North America 5 O:2,3 II Hare, goat, sheep, Europe, Australia rabbit, monkey Y. enterocolitica and Y. pseudotuberculosis can be divided into numerous serotypes on the basis of antigenic variations in cell-wall lipopolysaccharide (LPS). Aleksic and Bockemühl (17) have proposed a revised and simplified typing scheme, which includes 20 antigenic factors for Y. enterocolitica alone. Serotype O:3 is most frequently isolated from humans in general (18–22). Other common serotypes obtained from humans include serotype, serotype O:9 and serotype O:8. However, several O-antigens, including O:3, O:8, and O:9, have been found in pathogenic and nonpathogenic strains (23). An accurate biochemical characterization is needed before or after serological typing that leads to correct assessment of the relevance of strains especially from foods and the envi- ronment, because related species and biotype 1A strains are widely distributed in these samples (24). The bioserotypes Y. enterocolitica differ in their geographical distribution, ecological niches, and pathogenic properties. The vast majority of clinical isolates belong to a relatively few bioserotypes. These bioserotypes have different geographical distributions (Table 3). Strains of biotype 1B serotypes O:4,32; O:8, O:13; O:18; O:20 and O:21 are frequently found associated with human diseases, mostly in the United States and Canada (25),but bioserotype 1B/O:8 has occasionally also been found in Japan and Europe (26–30). Strains that are largely responsible for human yersiniosis in Europe, Japan, Canada, and the United States belong to bioserotype 4/O:3 (25). Bioserotype 3/O:3 has been recovered in Japan (31) and China (32); serotypes O:9 and O:5,27 are more widely distributed (33). Non- pathogenic strains of biotype 1A (e.g., serotypes O:5; O:6,30; O:6,31; O:7,8; O:10, O:18; O:46 and nontypable trains) are distributed worldwide and are predominantly isolated from the environment, water, feces, and food (25). 82 Fredriksson-Ahomaa Table 4 Distribution of Serotypes O:1 to O:5 of Y. pseudotuberculosis Isolated From Human and Nonhuman Sources No. of Country Source isolates 1a 1b 2a 2b 2c 3 4a 4b 5a 5b Ref. Japan Human 272 30 11 18 6 9 4 11 26 54 (42) 4 Pig 195 28 7 10 10 40 2 1 7 Dog 40 12 2 1 1 2 17 5 Cat 19 2 1 1 4 11 Rabbit 16 3 1 1 2 9 Rat 8 1 7 Water 39 2 2 2 12 5 16 Japan Human 45 14 1 2 28 (247) Raccoon dog 23 3 2 17 1 Wild mouse 9 2 7 Deer 8 1 6 1 Japan Water 110 9 5 2 1 14 19 54 6 (84) Italy Human 5 5 (127) Pig 8 1 7 Germany Human 52 21 10 7 3 7 2 2 (40) Hare 35 17 8 5 1 4 Bird 19 11 4 3 1 Sheep 5 2 2 1 Cat 5 2 2 1 Deer 4 1 1 2 Pig 3 1 3 Belgium Human 8 4 2 2 (124) Y. enterocolitica can also be divided into phage types. Two schemes (Swedish and French) are used for phage typing of Y. enterocolitica (34). Of these, the French scheme has been used frequently and it recognizes 12 phage types: I–X (including IXa–c). The Swedish scheme recognizes seven phages (A1, A2, B1, B2, C32, C61, and E1) and is used less frequently. Neither of these schemes has produced a large number of distinct epidemiological types because many strains fall into the same phage types. Strains of bioserotype 4/O:3 and phage type VIII predominate in Europe and Japan (35), whereas phage type IXb has been isolated in Canada (36) and in the United States (37). Y. entero- colitica of bioserotype 1B/O:8 and phage type X, which is a typical North American type, has also sporadically been isolated in Japan (28,30). Because of the need to maintain stocks of biologically active phages and control strains, phage typing is available at only a few laboratories. A simplified antigenic scheme for serotyping of Y. pseudotuberculosis consists of 15 O-serotypes of which serotypes O:1 and O:2 are divided into three subtypes a, b, and c; and serotypes O:4 and O:5 into subtypes a and b (15,38). The serotypes of Y. pseudotu- berculosis differ in their geographical distribution and ecological niches (Table 4). Yersinia 83 Serotypes O:1b and O:3 of Y. pseudotuberculosis have been isolated from the patients in Canada (39), whereas serotypes O:1a, O:1b and O:3 have most often been found in humans in Europe (40,41). In the Far East, serotypes O:1b, O:2a, O:2b, O:3, O:4a, O:4b, O:5a and O:5b, of which O:4b and O:5b are dominant, have been isolated from clinical samples (16,42).